Generating and controlling system for radiotelephones



Dec. 7 1926. 1,610,090

' v. A. HENDRICKSON GENERATING AND CONTROLLING SYSTEM FORRADIOTELEPHONES Filed Nov. 1 1922 Patented Dec. 7, 1925.

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VERNER A. HENDRIGKSON. GE .SPEINGDALE, CONNECTZCUT, ASSIGNOR OFONE-THIRD T0 FRED IBERG3-OF STAMIEORD, CONNECTICUT, AND ONE-THIRD T 0 J.EDWARD BROWN, OF SPBINGDALE, CONEECTICUT.

GENEBATENG AND GON'TROLLZLNG SFZ-EiTEM FOB RADIOTELEPl-IONES.

Application filed November 14, 192-2. Scrial No. 600,867;

My invention relates to electrical signal transmitting apparatus andmore particularly to generating and controlling systems utilized in thetransmission of intelligence by radio telephony, V

The primary object of my invention isto provide a radio transmittingsystem of greater efifectiveness than, has heretofore been common in theart. Further objects are to augment the economy of operation of suchradio transmitters, to provide controlling instrumentalities which aresusceptible of easy adjustment, and to improve the accuracy of speechtransmission and reproduction. Moreover, my invention involves noelements which are erratic in operation or difficult of manipulation andconsequently as r a whole it is eminently suitable for continuous andpractical service.

I have discovered that by designing the several portions of a radiotelephone system along the novel lines described in the followingspecification, and by arranging the component parts into aharmoniously-operating whole, the apparatusbecomes capable oftransmitting radio telephonic signals over great distances with theapplication and consumption of only small or moderate amounts of power.Also, I find that by properly proportioning and arranging the controlc1rcuits of my transmitter, this unusually economical transmission canbe attained without losing accuracy or fidelity of reproduction of thetransmitted speech.

The construction and operation of my systern may be more clearlyunderstood by reference to the drawing, which is a conventional wiringdiagram of one form of thetransmitter which I prefer to employ. In thisdrawing I'have not shown mechanical details such as the methods ofmounting; it will be understood by those skilled in the art that greatlatitude may be allowed in such matters without departing from thespirit or losing the utility of my invention. The various elements areindicated by their usual diagrammatic representations, and the drawing,in connection with the following description, will serve to define to aradio engineer the exact character and arrangement of apparatus,embodying my invention, which I have found to give satisfactory results.

Referring specifically to the drawing, it-

will be seen that the transmitting system may conveniently be consideredin five portions, viz, the control, the voice amplifier, the modulator,the oscillator and the radiator. Certain elements, in particular thepowersources, are common to several of these arbitrary divisions, butthe general opera-v tion of each part may be analyzed independently ofthe others.

The control system comprises the microphone M, into which are spoken theWords to be transmitted, the direct current source El whose output ismoulded into electric undulations (corresponding to the sound waves. orspeech) in passing through the microphone M, the modulation transformerMT and the leak resistance R1. The source El may conveniently be al-volt battery and the microphone M a standard long-distance telephonetransmitter. -T he transformer MT should be designed to develop themaximum potential variation possible without int-roducing distortion; Ihave found that a primary to secondary impedance ratio of 60 to 600OOOohms is satisfactory, and that a substantial improvement in qualityof speech reproduct on may be obtained by connecting the non-inductiveleak. resistance R1, of

about one megohm,'in shunt to the secondary have a voltage of slightlyover 20 and must have its negative terminal connected to the grid. Thisbattery serves to maintain the grid at a potential substantially morehighly negative than any part of the filament, and this not onlyprevents energy loss by reason of current flowing across the vacuousspace from the grid to the filament but also minimizes distortion of theamplified speech-carrying currents.

The filament of thevoice amplifier tube VA is heated by current from thebattery Ea passing through the rheostat R4: which regulates the degreeof incandescence of the filament. Battery E l may be a group of 1storage cells in series, delivering continuously about 2 amperes at 8volts potential difference. The negative terminal of this battery shouldbe connecting to earth, as shown. The rheostat R 1 may have a totalresistance of about 10 ohms.

The plate circuit of the voice amplifier tube VA is supplied with directcurrent energy from the generator DC, to the positive termiual of wiichit is connected by Way of the non-inductive resistor R2 and theimpedance coil 12. The negative terminal of the generator DC isconnected to earth, thus completing the filament-plate circuit of thetube VA. This generator produces current at a potential of from 700 to1000 volts, for the larger tubes of the system; the voice amplifier tuberequires only from 350 to 500 volts on its plate (positive with respectto the filament) and consequently r prefer to reduce the potentialapplied in this circuit by inser'ing the resistance unit B2. In generalthe unit R2 has a resistance approximately equal to that of the tube, orin this case about 10,000 ohms. The plate current, under theseconditions will be about 40 millian'iperes normal, which increases to 50or 55 milliamper-es when speech is transmitted.

lt will be understood that voice-controlled undulating currentsreproduced by the microphone and battery El will be increased inpotential by the transformer MT and applied to the grid or controlelectrode of the voice amplifier tube VA. The magnifying function ofthis tube will result in augmented variations in the plate circuitcontaining the retistance R2 and the choke coil or impedance T2. Theinductive reactance of the coil 12 will prevent dissipation of thesevariat-ions in the plate circuit and will cause the impression ofintense fluctuations of potential upon the coupling condenser FCS whichleads directly to the input circuit of the modulator vacuum tube MO.

This modulator tube is the heart of the third portion of my transmitter,and may be (in the particular instrument herein described) a standard 50watt audion power tube. As shown in the drawing, its grid is connectedto ground through the leak resistor R3, which may have a value of from10 to 15 thousand ohms, and the battery E3. The battery E3 impresses aconstant negative potential on the gridof the modulator tube, and mayconveniently have an electromotive force of 40 volts.

The filament of the modulator tube may be heated by means of alternatingcurrent supplied from the ordinary lighting lines shown at A0. Thispower source is connetted through the switch SVV' to the primary P of astep down transformer ST, the secondary terminals of which are applieddirectly across the filament of the modulator tube MO. This transformershould be constructed to reduce the AC voltage of the line (which isusually of about volts) to a value of approximately 10.5 volts, which issuitable for thefilament circuit. I prefer to ground the mid point ofthe seconcary of tnis step down transformer, and to connect across eachhalf of the secondary coil thus divided a fixed condenser (shown in thedrawing at FC l and FCF) of about 0.001 microfarad capacita .ce. It willbe seen that the filament is effectively grounded for direct currentthrough the windings of the transformer secondary and that by the pre--;...:ion of the condensers l Ce and PS5 it also effectively groundedfor radio frequency oscillations, which are enabled to pass around thesecondary winding toearth directly through these condensers. On theother hand, these condensers are of quite high impedance to alternatingcurrent variations of audible frequency, as is also the secondarywinding of the step down transformer, and it is to this novel balance ofelectric constants that I attribute substantial portion of the superiorresults obtained by the use of my system.

. The plate circuit of the modulator tube MO is supplied with aboutmilliamperes of dir ct current at from 700 to 1000 volts, directly fromthe high potential generator DC, the negative terminal of which isgrounded, its positive terminal being led to the'plate of the modulatortube through the impedance coil T1. For this coil, as well as for theimpedance 12' I- prefer to use a closed iron-core choke coil having aninductance of approximately two henrys.

The intensified voice current potential variations applied to themodulator tube grid through the condenser F03 serve to control theeffective plate resistance of this mod lator tube throughout a widerange. As shown in the drawing, the high potential point of themodulator plate circuit is connected directly to the plate of theoscillater tube OS through the high frequency choke coil HFC andsupplies this tube with its normal plate current of about 125milliamperes. This coil, having an inductance of about 3 millihenrys,effectively prevents the leakage of radio frequency oscillations throughthe modulator tube, but permits the varying resistances of the modulatorto abstract from, or, by reason of the reactance of 11, to feed into,the oscillator plat-e circuit (at audible frequencies) varying amountsof electric energy at a rate which depends entirely upon theinstantaneous intensity of the voice vibration to be transmitted. Itwill be seen at once that if the as though the modulator were entirelydis-' connected. Intermediate values of modulator tube resistance(produced by lntermediate values of the applied voice currents) willresultin intermediate values of the generated radio frequencyoscillations, and thus of the intensity of the radio frequency currentsproduced in the antenna circuit. Consequently the intensity of the radiowaves transmitted may be exactly and quantitatively controlledthroughout a wide range by the speaking voice or by other sounds whichimpinge upon the microphone M. Stored energy in the impedance I1 may, ona sudden increase of modulator tube resistance, practically double theoscillator plate voltage for an audible frequency period. V I

The filament of the oscillator tube OS is connected in parallel withthat ofthe modulator tube MO and supplied from the alternating currentsource which has already been described. I prefer to use a 50 watt poweraudion for the oscillator as well as for the modulator; as-will be seenfrom the drawing this filament circuit is grounded through the step downtransformer secondary and the condensers FU L and FC5 ex actly as in thecase of the modulator tube The oscillator plate circuit is fed-withdirect current from the sourceDC through the choke coil I1 and the highfrequency coil I-IFC, the return path being through the groundconnections of the generator and oscillator filament. From theoscillator plate a branched oscillating circuit .to ground is providedthrough the'fixed condenser F02 (which may have a capacitance of about0.002 microfarads) and the branch resonant circuit consisting of theelements L1 and V02. rangement L1 is a variable tuning coil ofapproximately 0.09 millihenry maximum inductance, and VC2 is a variablecondenser having a range up to about 0.00025 microfarad capacitance.Such a coil may be made by winding 16 turns of #18 wire on a 4 inchdiameter cylinder. It will be understood that the constants here givenhave been chosen for operation at comparatively short wave lengths, inthe neighborhood of 200 meters. From the branch resonant circuit justdescribed a connection is made directly to ground The antenna-to-groundcircuit is inductively coupled to the coil L1 In my preferred arthroughthe secondary coilrL2, one end of which leads directly to ground and theother end of whlch is connected through a tuning condenser VCI and aradio frequency ammeter RFA to the antenna A. The coil L2 andthecondenser VCl must be chosen with regard to the constants'of the aerialwithv which they are to be used; with an antenna having a capacitance of0.00038 microfarad I found that the condenser VCl should extend upward"to a maximum of 0.0004 microfarad and that the inductance L2 may have avalue of 0.03 millihenry, which may be secured by winding let turns of#18 wire, somewhat spacedpupon a,

tube of 4% inch diameter.

Oscillations generated in the plate'circuit inductance L1 will beinductively transferred to the aerial circuit coil L2, thus re-. sultmg(when the antennaclrcuit is tuned) in a substantial radio frequencycurrent be tween aerial and ground, As is well known, such a currentgives rise to thedesired electro-magnetic waves which are to betransmitted.

The grid circuit of the oscillator OS extends to ground through thevariable coil L3. and the fixed condenser FC,,which latter is shuntedbya leak resistor R5. .The

coil L3 is inductively coupled to the an-- tenna coil L2, and isadjusted in conjunction with the condenser F01 so as to control theoscillator grid potential in such phase and intensity that electricoscillations will bemaintained in the plate and aerial systems. I havefound that L3 may conveniently be a coil similar to that described forthe plate circuit L2, and that the condenser F01 should have acapacitance of about 0.002 microfarad. The resistor R5 may convenientlyhave a value of approximately 5000 ohms; its function is mainly toprevent the oscillator grid from attaining a hlgh negative charge whichwould choke the oscillator system.

The operating adjustments of my system are notably simple and stable andmay be easily determined by noting the type of operation which ischaracteristic of the various parts when properly co-ordinated. AlthoughI have given in the foregoing a number of numerical values of variousconstants which I have found by experiment to be suitable for aparticular transmitter operating at approximately 800 volts oscillatorplate potential and delivering 2.8 amperes into a 12-ohm antenna at 1500 000 cycles, it will be understood that I do not wish to beunderstood as limiting my invention to the particular constants cited,nor even to the specific circuits illustrated. Indeed, manymodifications will at once occur to one skilled in the art; for example,the power may be changed by the choice of vacuum tubes of sizes largeror smaller than those cited in the above (the circuit constantsnecessarily being changed to correspond with the altered powerconditions) or operation may be effected atv-ravelengths quite ditlercntiron'i tl-iat chosen in the example given. Further, it is feasible touse other terms of oscillation circuit, common in the art, inconjunction with the voiceainplitier and modulator l l we illustrated orto utilize radio irequeney ainglifiers between the oscillator and thesystems for the purpose of augmenting the output po l l hatcver circuitvariations are made, it is essential to maintain the proportions of theVilllDUS choke or ire e *e coils and condensers such that they willoricr suitable reactance to the currents oi various frequenciesdeveloped in the several parts of the system, as exemplified in theforegoing.

l have it und certain easily observed for. tures to be characteristic ofnsystem -when used under the conditions set forth. These are generallyapplicable, though to, varying Xtents the circuits are modified. toarrangeinents which embody my invention, and may be stated as follows:

A. The plate current of the voice-amplifier tube increases when themicrophone is spoken into.

B. As the voice amplifier plate current in creases, the averagemodulator tube plate current decreases as may be shown by its change ofcolor from cherry-red to black or grey.

C. As falls oil, the oscillator plate current in oral increases.

1). It the radiating-load of the aerial circuit is Withdrawn, the totalplate curren' though oscillator and modulator tubes rails to as littleas its normal value.

E. The intensity of modulation is so great as to produce mechanicalvibration oil? the oscillator tuhe, so that the transmitted sounds canbe heard reproduced in the air Within a zone of several feet about theoscillator.

F. The use of alternating current for heating the filament oi themodulator and oscillator tubes, together with the system of audioimpedances and radio "frequency byment heating.

It Will be understood that in the speci'iication and claii lhave usedthe terms audio frequency and radio frequency in their normal senses, i.e., audio frequency refers to the rate of electric variations corresponding to the sounds to be transmitted rily between the limits of 15 cycles20 000 cycles per second) and radio frequency refers to the rate ofelectrical oscillations to be radiated as electromagnetic v (ormnbetween the limit-sot it) 000 and 3 ace 0 cycles l or second). I do notdesire to be limited to any specific numerical values of her frequency,but in general intend that lie frequency shall s' the cy of the carrierWave ur frequency the trequencyot' the mod arions in osed thereon.

aving set forth the novel and useful rewhich may be obtained from radio1 .[lSDIl'tiBlS embodying my invention, and having described in detheconstruction auo operation of one pr ctical orni of such transmitters,what I claim is:

A radio-telephone oscillator comprising a- O neantenna, groundconnection, a condenser an inductor serially connected between i antennaand said ground connection, a

vacuum tube hz ving a cathode, an anode and condenser in shunt to saidsecond inductor. a third inductor couplec to said fiiStdlZtTflQCiinductor and connected in said control ele"- trode circuit, a fourthcondenser in series therewith in said circuit, a resistor in shunt tosaid fourth condenser, and means for varying the electrical constants ofthe circuit thus constituted, substainia ly as described.

VERNER A. HENDRICKSON.

(ordinai yri 'l1 said second in luctor 1n said anode circuit, third

